This invention relates to a filter system and specifically to a system utilizing solid and liquid reagents.
It is conventionally known to use activated charcoal and other materials as adsorptive elements to remove impurities from an air stream. With the advent of effective fiber cross sections, it is possible to produce fibers which are partially hollow. A particularly effective cross section is one having three T-shaped lobes extending from a central core, as described in U.S. Pat. No. 5,057,368, xe2x80x9cFilaments Having Trilobal Or Quadrilobal Cross-Sectionsxe2x80x9d to Largman et al., which is incorporated herein by reference. Conventional filters have used filtering media coated with solid or liquid materials in a variety of applications; however, many of these applications have relied on absorption, rather than adsorption. Adsorption occurs where particles to be removed attach to the surface of the filter material elements; whereas, absorption occurs where molecular motion mobility is harnessed to move unwanted particles from one zone to another in a non-mechanical manner. The multilobal fiber has been particularly effective as a wicking fiber where certain contaminant-removing liquids or solids are filled in cavities formed within the fiber.
The multilobal fiber filled with solid filtering particles have been used in adsorptive air filtration and odor-removing applications. Such filtering particles have included the use of carbon particles, zeolites, baking soda, cyclodextrins, and solids which could adsorb certain contaminants (see U.S. Pat. No. 5,759,394, which is incorporated herein by reference). Other applications utilizing multilobal-type fibers as wicking fibers also have involved absorptive properties of certain liquids which are filled within the cavities of the fibers. These liquids were typically chosen to lightly absorb odor and gas molecules in a reversible manner from a contaminated air stream to aid in the eventual dispersion of these molecules into a second air stream (see U.S. Pat. Nos. 5,891,221 and 5,704,966, which are incorporated herein by reference).
Maintaining environments free of contaminants is particularly critical in the manufacturing of integrated circuits because wafers are very susceptible to small particles and low levels of certain chemicals. This can be done by manufacturing wafers inside clean rooms with filtered air. The filters are used to reduce particle and chemical levels to extremely low levels (less than 1 part-per-billion). Semiconductor tools are also sometimes equipped with environmental controls that provide local ultra clean airflow during processing. However, conventional chemical filters have a very short life span, require frequent replacement, and are ineffective at efficiently filtering out certain chemicals.
The priority application teaches filtering of basic gases using fibers having longitudinally extending internal cavities that contain a reagent that chemically reacts with the basic gas. Preferred reagents include an acid, a coordinating agent, a complexing agent, and a deliquescent agent, and may advantageously be impregnated into an adsorptive solid. At the time, it was not recognized that basic gases could also be filtered using an oxidizing reagent, or that acidic or neutral gases could be filtered in an analogous manner. Thus, there is still a need to provide devices and methods for filtering various gases.
The present invention provides devices and methods in which a gas contaminant is filtered using fibers having internal cavities that contain a chemically reactive oxidizing agent, a hydrogen ion acceptor or donor, a coordinating agent, a complexing agent, or a deliquescing agent.
The gas contaminant may be acidic, basic, or pH neutral. Where the contaminant is basic, the reagent can be any acid, but is preferably an oxidizing agent. Where the contaminant is acidic, the reagent is preferably basic, and more preferably comprises a group 1 or group 2 metal cation, preferably of the following anions: a phosphate, chitosan, a hypochlorite, a borate, a carbonate, an hydroxide, or oxide. Where the contaminant is neutral, the reagent is preferably a complexing agent, a coordinating agent, an oxidizing agent, or a deliquescing agent.
In preferred embodiments the reagent comprises a metal cation, especially a group 1 or group 2 metal cation. The reagent may also advantageously comprise a phosphate, chitosan, a hypochlorite, a borate, a carbonate, an hydroxide, or oxide The reagent is preferably impregnated into an adsorptive solid, including, for example, carbon powder, zeolite, aluminum oxide, or silica.
The fibers are preferably multilobal, and most preferably either trilobal or quadrilobal. It is also preferred that the fibers contain a plurality of T shaped lobes.
Various objects, features, aspects, and advantages of the present invention will become more apparent from the following detailed description of preferred embodiments of the invention, along with the accompanying drawings in which like numerals represent like components.